Internal combustion engines are widely used in virtually all types of powered vehicles, including automobiles, motorcycles, boats and aircraft. A major problem with internal combustion engines is the generation of waste heat, which must be efficiently transferred from the engine to the surroundings in order to avoid heat-related engine failure such as cracking, warping or degradation of the engine lubrication oil.
There are two common engine cooling techniques: air cooling and liquid cooling. Whilst air cooling was popular during the infancy of combustion engines, it is no longer widely used; liquid cooling is now the favored cooling technique for most combustion engines.
Air cooling involves directing air, typically at a high velocity, around the engine cylinder or cylinder block. Fins or other formations are typically provided on the outer surface of the cylinder or cylinder block in order to increase the surface area and hence enhance heat transfer.
In liquid cooling, the transfer of heat from the engine to the surroundings is via an intermediary liquid cooling circuit. A liquid coolant is passed through fluid passages defined within or around the engine cylinder or cylinder block, whereupon heat generated during the internal combustion process is transferred to the coolant. The coolant is then passed to a heat exchanger, commonly known as a radiator, having a large surface area exposed to the surroundings. As the coolant circulates through the radiator, heat is transferred from the liquid coolant to the surroundings. The cold coolant subsequently exits the radiator and is fed back to the engine cylinder or cylinder block to repeat the process. Alternatively, in an open circuit, the cooling fluid that exits the radiator may be disposed of and fresh cooling fluid fed to the engine cylinder or cylinder block.
In general, the liquid coolant utilized in liquid-cooling devices is water based but may comprise other agents such as antifreeze and/or corrosion inhibitors.
A cooling technique similar to the above-described liquid cooling may also be employed in relation to the engine lubricating oil. Cooling of the engine-lubricating oil is commonly known as “oil cooling” and comprises passing the engine oil from the engine to its own dedicated radiator and subsequently returning the oil to the engine. Oil cooling is generally employed in conjunction with one of the above-described air-cooling and liquid-cooling techniques i.e. the engine oil is typically not the principal coolant.
In order for liquid cooling and oil cooling to constitute effective engine cooling techniques, there must be efficient heat transfer from the radiator to the surroundings. In practice, this is achieved by providing the radiator with an array of fins or other formations in order to increase the surface area thereof, and by generating a high velocity air flow around and/or though the radiator.
One known technique for generating an air flow around or through a radiator is to rely on ram-air pressure provided by the forward motion of the vehicle. In such arrangements, air intakes are provided at the front of the vehicle and air received through these intakes is directed towards the radiator. However, one problem with this arrangement is that the cooling air flow is only generated when the vehicle is in motion. This can lead to overheating of the engine when engine is operational but the vehicle is stationary, for example when an aircraft is on the ground ready for take-off.
It is also known to direct air towards the radiator via one or more fans. The power required to operate the fans must, however, be provided by the engine, thereby increasing the total engine load and hence contributing to the heating of the engine. In view of the fact that the fans are provided for the sole purpose of cooling the engine, the side-effect of heating the engine represents a considerable failing in a fan-based engine cooling arrangement.